Fiat 1996 Brava Service Manual page 460

Engine
Fuel system
10.
Bravo-Brava I0i 16v
'98 range
LAMBDA PROBE (NTK 0ZA334-A1)
This is the sensor which measures the oxygen content in the exhaust gases.
The sensor's output signal is sent to the electronic control unit to adjust the air-petrol mixture, in order to
maintain the mixture's stoichiometric ratio as close as possible to the theoretical value.
To obtain an optimum mixture, the quantity of fuel injected must be as close as possible to the theoreti­
cal quantity which would be required to be fully burnt in relation to the quantity of air drawn in by the
engine.
X=
In this case the Lambda (X) factor is 1; in fact:
QUANTITY OF AIR DRAWN IN
QUANTITY OF THEORETICAL AIR REQUIRED TO BURN ALL THE INJECTED FUEL
VOLTAPF
mV
1000 -
8 0 0 -
6 0 0 -
4 0 0 -
2 0 0 -
0.980
RICH MIXTURES I
1.020
WEAK
MIXTURES
:t
0,7 0,8 0,9 1,0 1,1 1,2 1,3
AIR COEFFICIENT X
X= 1 Ideal mixture
The CO is within legal limits
X ^ 1 Weak mixture
Excess air; the CO tends to be low
X^ 1 Rich mixture
Lack of air; the CO tends to be high
NOTE While the coefficient X expresses the excess or shortfall of air supplied to the engine in relation
to the value theoretically required, the air-petrol mixture is a ratio between these two sub­
stances which, combined together, react chemically. For today's engines, this means that they
require 14.7-14.8 parts of air to burn 1 part petrol.
The probe is mounted upstream of the catalytic converter.
This consists of a ceramic casing (1) based on zirconium dioxide, covered with a thin layer of platinum
closed at one end, inserted in a protective pipe (2) and housed in a metal casing (3), which provides fur­
ther protection and permits assembly onto the exhaust manifold. The outer part (B) of the ceramic is ex­
posed to the exhaust gas current, while the inner part (A) communicates with the ambient air.
The operation of the probe is based on the fact that at temperatures exceeding 300°C, the ceramic mate­
rial becomes a conductor of oxygen ions. Under these conditions, if the quantitiy of oxygen on the two
sides (A and B) of the probe is in different percentages, a voltage variation between the two ends is gen­
erated, which is an indicator of the difference in quantity of oxygen in the two environments (air side
and exhaust gas side).
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Publication no. 506.670/14